Subdivision To Preserve Low Poly Style
Have you tried the Edge Split Modifier?
It does the trick for me.

This is an Ico-Sphere. I added the Edge Split Modifier to it, then I sharpened all the edges (or just the ones between which there should be no interpolation of normal values), then I added Subdivisions with Mesh > Subdivide, Slices set to 1 and Smoothness to 0, like suggested.



The UVs split as they should.